1. Field of the Invention
This invention relates to methods and means for selectively controlling the movement of crawling insects and more particularly to non-toxic, non-debilitating methods and means for causing crawling insects to abandon the site they have infested or for discouraging crawling insects from infesting a site where they are not wanted.
2. Discussion of the Prior Art
The crawling insects of the type with which this invention is concerned are those which are pests or nuisances to man. These include, for example, gypsy moths that crawl from the ground up into trees to devour the leaves of the trees; cockroaches, spiders, scales and palm aphids which are often offensive in appearance and may carry and spread disease; and, perhaps the most widespread and annoying of the general group, is the ubiquitous ant. The ant exists in many forms including the destructive leaf eater, Argentine, carpenter and pharaoh ants, the termites and, of course, the militant and destructive fire ant. Fire ants may cause havoc, particularly in the warmer climates, by infesting various electrical apparatus such as transformers and switch boxes and, because of their aggressive habits and acidic residues, cause breakdowns of the insulation and destroy the electrical operation of a device. Ants may be attracted to electrical devices because of the magnetic field created by the alternating current and perhaps by the warmth and shelter provided in the interior of an electrical device.
Many pesticides and insecticides are available which will kill or disrupt the life cycle of crawling insects, but essentially all of them are environmentally objectionable because of their toxicity. Their toxicity also may be of danger to animals and humans and prevent their use in applications where the pesticides may come in contact with food or otherwise present the danger of ingestion. This prevents them from being used in applications where food may be present, such as in dining rooms, kitchens, picnic tables, pet food dishes and the like.
Pesticides and insecticides are also less than ideal in function when used in an outdoor environment in which they may be washed away or otherwise rendered ineffective when exposed to the elements.
A number of crawling insect traps are disclosed in the prior patent art that utilize surfaces that have been treated to make it difficult for insects to crawl over the surfaces. Typically, these traps have a vertically disposed surface that the crawling insects must crawl over in order to get out of the trap. By one method, a sticky substance is spread over the surface which entraps the insect, much like fly paper, or, by an alternative method, a vertical surface is made slippery to the crawling insect so that if loses its footing and slides into the trap.
An early attempt to make an insect trap with a slippery vertical surface is disclosed in U.S. Pat. No. 400,460 where there is shown a trap in the form of an open topped box fitted with inwardly and downwardly slanting sidewalls. The upper portions of the slanting sidewalls are covered with a moderately rough material, such as paint, paper or cloth, and immediately subjacent this surface is a polished surface that, it is said, causes the insect, Upon leaving the comparatively rough surface, to lose its footing, slide down the polished surface and fall into the bottom of the trap.
Variations of the U.S. Pat. No. 400,460 in which a slippery vertically disposed surface is used appear in the prior patent art in U.S. Pat. No. 1,667,048 in which a slippery glazed surface is used; U.S. Pat. No. 2,167,978 in which the vertically disposed surface is treated with a powder that adheres to and renders ineffective the cupolas and cleaving balls of insect's legs; U.S. Pat. No. 3,851,417 in which a slippery film is made from a mixture of lanolin and linseed oil; and U.S. Pat. No. 4,030,233 in which a slippery surface is provided by soaps or other fatty substances. Representative of the sticky substances method is U.S. Pat. No. 2,606,391 which discloses a hydrophilic, non-drying, high viscosity gel to entrap a crawling insect.
U.S. Pat. No. 4,263,740 is of interest since it discloses an insect trap having inwardly and downwardly sloping side walls which are covered with a loosely adhering particulate material. The particulate material is so loosely held that it will break loose and "avalanche" downward when an insect attempts to cling to it. The operation of the trap mechanism requires that the insect first crawl across the coating so that the particulate material, in the preferred range of from 100 to 300 microns, will cover and adhere to the insect's pulvilla and destroy the effectiveness of the pulvilla in sticking to a smooth surface. The patent teaches that when the insect reverses its direction in an attempt to crawl up the slanting sidewall and escape from the trap, the insect must grip the particulate material with its tarsal claws. Since the particles are only loosely adherent, they break away creating an "avalanche" that falls with the insect into the interior of the trap. The particulate material disclosed in this patent is either organic or inorganic and as examples Teflon(.RTM.), sand, clay, ground pyrophyllite, aluminum silicate, cellulosics, talc, sand, and flour are given.
Entomologists sometimes use similar techniques as discussed above relative to the prior patent art to contain their experimental insects within laboratory vessels. Thus they have coated the inside walls of their vessels with sticky substances, most commonly Vaseline(.RTM.) and mineral oil, to prevent insects from escaping but this method suffers from the fact that the insects are entrapped and die. Similarly, coatings of talc have been adhered to the side walls which prevent the escape of insects by smothering them, but this also kills the insects.
To avoid killing their specimens, entomologists have also used the slippery surface technique by coating the interior side walls of vessels in which they keep their experimental insects with water dispersions of polytetraflouroethylene. After one or more coatings are applied as by painting a wide band on the side walls, many crawling insects are unable to climb the side wall and are thus contained within the vessel. These coatings are fragile and do not adhere well to the side walls which restricts their utility to the controlled environment of a laboratory where the coating can be protected from accidental damage as by scratching or bumping. It can be understood that if a portion of the coating cracks or is sloughed off, sites are established which enable an insect to obtain a grip and advance up the side wall of the vessel. Further, when exposed to water, these slippery coatings wet out and lose their effectiveness in preventing the escape of insects. To overcome these shortcomings, the slippery coatings which have been used by entomologists require frequent renewal and they are applied in very wide bands, relative to the length of the insects, to make up for the imperfections that develop in the coatings.
The present invention is related to the above described prior art in that it relies upon skewed treated surfaces to prevent the movement of crawling insects over the surfaces but, unlike the prior art devices, selectively controls the movement of different sized insects and, rather than confining the insects within a given trap or perimeter, either prevents the crawling insects from entering a given area that is to be protected or causes the crawling insects to abandon an area which they presently are inhabiting.
The methods and means of the present invention also represent an advance over the prior art in that the coatings are more adherent to their substrates, they are more durable and longer lasting, they are less subject to losing their effectiveness due to the effects of water, they can be more readily and efficiently applied and they do not have to be applied in bands as wide as those of the prior art to ensure their effectiveness.
The present invention is further distinguishable from the prior art in that it discloses coating formulations and methods for their application that greatly increase the effectiveness of the methods used by the prior art to contain or trap insects.
Accordingly, it is an object of this invention to prevent crawling insects from infesting certain areas.
A related object of this invention is to cause crawling insects to abandon an area which they have previously infested.
Another object of this invention is to protect areas from infestation from crawling insects without using insecticides or toxic substances that may be harmful to the environment.
Another object of this invention is selectively to control the type or size of crawling insects which enter or leave an area.
Another object of this invention is to control the movement of crawling insects without harming the environment or injuring the insect.
Another object of this invention is to provide for the creation of an environment which is not hospitable to crawling insects and cause them to leave and establish their nests elsewhere.
Another object of this invention is to provide coating formulations and methods for their application which will control or induce the movement of crawling insects.
Another object of this invention is to provide wearing apparel such as shoes and boots, ankle protectors, outer garments and the like which will prevent crawling insects from climbing onto the human body.
Another object of this invention is to prevent insects from crawling up the legs of furniture.
Another object of this invention is to provide methods and means for the control of the movement of crawling insects which are simple to use, are effective in relatively small amounts, remain effective over prolonged periods of time, are capable of withstanding moderate abuse, and are not rendered ineffective when contacted with water.
Another object of this invention is the provision of methods and means to control the movement of crawling insects that are capable of use in an exposed, outdoor environment.
Another object of this invention is to preserve the operational effectiveness of the electrical contacts in various types of electrical devices by preventing them from being overrun with insects.
Another object of this invention is to provide a liquid and a method of spraying it onto a surface in order to form an adherent film that is uniform in thickness and will not crack or crater.
These and other objects of this invention are achieved by dispersing finely divided, non-tacky particles of less than about 10 and preferably less than about 0.5 microns in a liquid; spraying or otherwise applying a smooth, continuous, holiday and bubble free coating of the dispersion over a surface; and drying the dispersion to form a coherent film which cannot readily be washed or wiped away. As is discussed in more detail below, a surfactant is often helpful in establishing the dispersion even though, in many applications of this invention, it may prove desirable to wash the film after it has been formed and remove residual surfactant from the film.
In the practice of this invention it has been found that crawling insects, such as ants, termites, gypsy moths, cock roaches and the like cannot climb on the coated surfaces when the surfaces are set at an angle to the horizontal. The minimum angle required to impede the progress of an insect over a surface coated in accordance with this invention is not a precise number of degrees as it will vary with the characteristics of the insect such as its size, whether it has any sticky substances on its legs, whether its tarsi have claws, and in the case of crawling pests such as caterpillars, how many legs it has. Nonetheless, as a generality, it may reasonably be estimated that surfaces treated in accordance with this invention should be skewed at least about 20 degrees to a horizontal axis to be effective. For purposes of this specification and the appended claims, the term "skewed surface" will be used to describe a surface that makes at least a 20 degree angle with the horizontal plane.
By way of example, if it is desired to keep gypsy moths out of a tree, the trunk of the tree may be coated with a circumferential band of the film forming substance of this invention. It has been found that when a surface to be treated is either too rough or porous, like the bark of a tree or the surfaces of wood, bricks, cinder blocks or the like, it is difficult to coat the bark (or other rough or porous surfaces) and effectively prevent insects from climbing the tree. This problem may be overcome by several means including painting the bark of the tree at the area to be treated with a sealant to provide a better surface to which the film forming material of this invention can be adhered. By another means, the film-forming materials may be first coated on the surface of a flexible base material which is then tightly wrapped around and adhered to the bark. And yet by another method a flexible web of material is adhered to the bark of the tree and the web is then sprayed or otherwise coated with the film forming suspension. One particularly convenient and effective material to use as a flexible web is cloth backed duct tape. It is intended that all of the above techniques are included within the scope of this invention.
It has been observed that the surface characteristics of the film forming materials of this invention may change when the film becomes wet with water. When a surface which has been prepared in accordance with this invention is exposed to the outdoor elements like snow, rain or high humidity, it may rewet and lose its effectiveness in preventing insects from crawling on its surface. It is believed that the tendency of the film to rewet is function of the surfactant used in preparing the dispersion and it has been established that the problem can be overcome either by not using a surfactant, by the selection of an appropriate surfactant or by removing the surfactant after the film has been formed. Some surfactants are naturally destroyed by exposure to the outdoor environment and UV light and others may be leached out of a film by washing the film with a suitable solution which, depending upon the surfactant, may include water, alcohols, acids, bases and the like.
The proper selection of the surfactant is initially of concern to obtain a uniform dispersion of the fine particles. The selection of the surfactant is important because it will influence the properties of the dry film including the strength of the film, the adhesion of the film to a surface, and the ease with which the film can be rewet. Further, if the dispersion is applied to a surface by use of an aerosol spray, care must be taken in selecting a proper propellent for use with a given surfactant since some combinations of propellent and surfactant result in the destruction of the dispersion.
The materials that may be used to form the dispersions of this invention must generally be less then 10 microns in diameter and preferably less than 1 micron to insure the formation of a film. (Here and elsewhere in the specification and claims, the dried residue that results when a dispersion of this invention is applied to a surface is referred to as a "film" since it appears to the naked eye to be continuous and since it is known that it will be effective in controlling the movement of insects only if it is free from discontinuities that can present a gripping point to an insect. On the other hand, this "film" may have little or no tear strength and, unless applied to an adhesive substance as is discussed below, the dried coating can not be peeled away from a surface without destroying the "film". For this reason, and since a better term does not come to mind, it should be understood that the term "film" as used herein may not be entirely consistent with some definitions of the term.)
It is important that the small particles selected for use with this invention do not have surface tack in the sense that they afford an adhesive point to help an insect traverse a treated surface.
The above criteria greatly limit the materials that are available for use in this invention. One suitable group of finely divided particles that have been found useful in the practice of this invention are synthetic plastics that can be prepared directly in minus 5 micron particle sizes as by suspension polymerization or dissolution and precipitation processes. It should be understood that, as a practical matter, it is difficult to grind plastic materials to the small particle size required in the practice of this invention. With this in mind, one class of materials that is particularly suitable for use in the this invention are the fluorinated hydrocarbons which can be prepared by suspension polymerization. This group includes polytetrafluoroethylene (PTFE), fluorinated ethylene-propylene (FEP) and perfluoroalkoxy (PFA). Suspension grades of fluorinated hydrocarbons are commercially available with maximum particle sizes of about 0.5 microns and others with average particle sizes of less than 0.2 microns. Since the fluorinated hydrocarbons have low coefficients of friction and are slippery to the touch they are most useful materials for use in the practice of this invention.
Other materials which are effective in the practice of this invention include suspension grade acrylics, precipitated nylons and inorganic materials with generally smooth surfaces that are available in diameters of less than about 5 microns. Examples of inorganic materials include powdered aluminum silicate, talc and carbon black.
As will be discussed in greater detail in the Examples that follow, there is a correlation between the particle size of the materials comprising the film and the size of the insect that can traverse its surface. As a general rule, the smaller the insect the smaller must be the size of the particles. As an example, if a mixture of 0.2 micron PTFE and 5 micron aluminum silicate particles are used to form a film, small ants can not crawl up the film whereas cockroaches can. If, on the other hand, the film is made entirely from 0.2 micron particles of PTFE, neither ants nor cockroaches can scale the film.
It has also been observed that certain crawling insects, particularly ants, find it necessary to crawl up onto the top surface of the mounds they build. If a number of stones, or relatively smooth, small rounded particles of most any material, are coated with a film of this invention and laid over on the top of an ant mound, the ants will desert the area and move their colony elsewhere. The same effect can be achieved if ceratin coated mechanical structures with skewed surfaces, such as of an egg crate design, are placed on the top of an ant hill. (For convenience, the stones, round particles and mechanical structures with skewed surfaces coated in accordance with this invention for placement on the top of present or prospective ant hills are sometimes hereinafter collectively referred to as "stones"). While the phenomena is not understood, it is presumed that the ants become frustrated when they are unable to climb and carry small particles over the stones to increase the height of their mound.
The above discovery can be utilized to considerable benefit where it is important to exclude ants from a location because of the mounds they build. Thus in the case of a ground level pad which supports an elevated transformer, a coating can be applied to the vertical cables or conduits leading from the ground upwardly to the transformer to prevent ants from climbing up the cables or conduits into the transformer. However, since the ants can still nest in the housing at ground level and erect mounds that potentially may obstruct auxiliary devices, a layer or two of round particles, such as small stones, can be distributed within the base of the pad and coated with the dispersions of this invention. In this manner the ants can neither climb the cables nor build mounds within the housing.
Another example of the benefit of placing stones with treated surfaces on the top of ant hills can be found in water meters that are located in housings at or slightly below ground level. These housings are often infested with ants which build large mounds that can completely cover the face of the water meter and prevent readings from being taken. The ants can be caused to leave the housing (or not enter it in the first instance) if smooth shaped articles, such as stones, are treated with the dispersions of this invention and placed within the housing in surrounding relationship to the water meter. Apparently, since the ants can't climb up onto the surface of the coated shaped articles carrying dirt with them to build a mound, they become frustrated and leave.